code: def __init__(
      self,
      main_pid: int,
      child_processes: List[subprocess.Popen],
      sleep_period: int = 5,
  ) -> None:
      super().__init__(
          daemon=True, name="child-process-observer"
      )  # thread stops if the main process exits
      self._main_pid = main_pid
      self._child_processes = child_processes
      self._sleep_period = sleep_period
      # Note: SIGTERM is not aggressive enough to terminate processes hanging in collectives
      self._termination_signal = (
          signal.SIGTERM if sys.platform == "win32" else signal.SIGKILL
      )
      self._finished = False
  
imports: import logging
  import os
  import signal
  import subprocess
  import sys
  import threading
  import time
  from typing import Any, Callable, List, Optional, Sequence, Tuple
  from lightning_utilities.core.imports import RequirementCache
  from typing_extensions import override
  from lightning.fabric.plugins.environments.cluster_environment import ClusterEnvironment
  from lightning.fabric.strategies.launchers.launcher import _Launcher
  from lightning.fabric.utilities.distributed import _set_num_threads_if_needed
  from lightning.fabric.utilities.rank_zero import rank_prefixed_message
label_desc: Use image node_id 1 to create a new _ChildProcessObserver object from inherited base classes: threading with example: obj = _ChildProcessObserver(main_pid, child_processes, sleep_period)